1. Field of the Invention
The present invention relates in general to a cleaning process. In particular, the present invention relates to a method of metal etching post cleaning, the application of which prevents damage to devices and effectively reduces cleaning costs.
2. Description of the Related Art
Generally, in semiconductor processing, methods of removing photoresist are wet stripping and dry stripping. Wet stripping uses chemical solvent to dissolve the patterned photoresist, and dry stripping uses high energy plasma to bombard the patterned photoresist or thermally remove the resist in oxygen atmosphere at high temperature (i.e. oxygen-plasma ashing).
It is possible to damage the substrate and metal exposed under the trench or via (contact hole) and profile of the trench or via by wet stripping. Accordingly, ashing has become the main method to strip photoresist in recent years. That is, the photoresist, in an oxygen atmosphere under high pressure and temperature, is oxidized so as to be eliminated by a vacuum pump. However, both polymer residue and accumulating charges are easily created on the surface of patterned metal layers during the metal etching and post cleaning, and are unfavorable for the next stage of the process. It is very difficult to completely remove the residual surface polymer using only plasma ashing because of insoluble metal oxides forming.
Accordingly, after conventional ashing is performed, it is necessary to use a cleaning agent such as ACT935 (organic amine solvent) to remove polymer residue. However, this agent creates higher costs.
Seeking to solve this problem, mixtures of sulfuric peroxide (e.g. 0.9M sulfuric acid and 1.18M hydrogen peroxide) and dilute hydrofluoric acid (DHF) are used as cleaning agents because of lower costs. However, this cleaning agent easily corrodes the metal in post-ash residue cleaning, thereby reducing the reliability of devices.
Therefore, the present invention is to provide a method of metal etching post cleaning performing another ashing by ozone (O3) to release accumulating charges. Moreover, the mixtures of 0.07Mxcx9c0.4M sulfuric acid (H2SO4) and 0.8Mxcx9c1.5M hydrogen peroxide (H2O2) are used as a cleaning agent to completely remove polymer residue and prevent damage to metal, thereby ensuring reliability of devices.
An object of the present invention is to provide a method of metal etching post cleaning to reduce the molar concentration of the sulfuric acid, thereby preventing damage to metal during post cleaning to increase reliability of devices.
It is another object of the present invention is to provide a method of metal etching post cleaning comprising an ashing by ozone to release charges created during metal etching post cleaning.
In accordance with the objects of this invention, a method of metal etching post cleaning is provided and includes steps of: providing a substrate with a surface covered by a patterned metal layer and a patterned resist layer in order; performing a first ashing to remove the patterned resist layer to expose the surface of the patterned metal layer; and cleaning the surface of the patterned metal layer with sulfuric peroxide, wherein the concentration of sulfuric acid and hydrogen peroxide in the sulfuric peroxide are 0.07Mxcx9c0.4M and 0.8Mxcx9c1.5M, respectively. In addition, the temperature during cleaning by the sulfuric peroxide is 25xc2x0 C.xcx9c50xc2x0 C. Moreover, the method further includes a step of performing a second ashing by ozone, wherein the treating time is 30 secxcx9c180 sec, and the treating temperature is 200xc2x0 C.xcx9c300xc2x0 C.